
which is so long that it can easily satisfy the current limit from the X-ray observations. Importantly, the misalignment mechanism can naturally produce the right amount of axion to explain DM in this case.
Also, the axion can explain the excess of electron recoil events observed in the XENON1T experiment through the axion-electron coupling \(g_{ae} \sim m_e/f_a \sim 10^{-14}\) .
On the other hand, if the axion accounts for about \(10\%\)  of DM, it can explain not only the XENON1T excess, but also various stellar cooling anomalies simultaneously [1]}. Such interesting axion scenarios can be explored by future X-ray observations such as Theseus [2]}, [3]}, Athena [4]}, eROSITA [5]}, and XRISM [6]}.
